Oligonucleotides are known that are substituted at the base moiety with fluorescent dyes such as pyrene and perylene (Non-patent Document 1). These oligonucleotides can be seen as clusters of fluorescent dyes since the fluorescent dyes are arranged along the nucleotide backbone. It is known that when an oligomer having a sequence of multiple fluorescent dyes of the same or different kinds is excited at a single excitation wavelength, fluorescence may be emitted in wavelength bands longer than those of the constituent monomers, or the fluorescence wavelength may vary depending on the sequence of fluorescent dyes. Therefore, it is thought that different detection targets can be detected by their different fluorescent color emissions at a single excitation wavelength by using multiple clusters with difference fluorescent dye sequences as fluorescent labels.    Non-patent Document 1: Kool et al., J.A.C.S. 129, 15426 (2007)